US3870863A

US3870863A - Electrical heating element for bread toaster or the like

Info

Publication number: US3870863A
Application number: US339915A
Authority: US
Inventors: Helmut Ohnmacht
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-03-11
Filing date: 1973-03-09
Publication date: 1975-03-11
Anticipated expiration: 1992-03-11
Also published as: FR2175783B1; IT977522B; ES412526A1; FR2175783A1; DE2211911A1; DE2211911B2; GB1421592A

Abstract

In a heating element for a toaster the heating conductor consists of a wire wound on a core of low thermal expansion coefficient. The conductor is carried by a frame including opposite support strips between which the conductor is strung in loops without intermediate support. The core consists of twisted threads of mineral fiber. A two-compartment bread toaster needs only three such elements; the heating conductor loops of each outer element may be provided on one face only and those of the central element may be wound about both faces.

Description

States aternt [191 ()hnrnacht [451 Mar. 11, 1975 ELECTRICAL HEATING ELEMENT FOR BREAD TOASTER OR THE LIKE [75] Inventor: Helmut 0hnmacht,D-6744,

Germany [73] Assignee: Fritz Eichenauer, Kandel, Germany [22] Filed: Mar. 9, 1973 [21] Appl. No.: 339,915

{30] Foreign Application Priority Data Marv 11, 1972 Germany... 2211911 [52] U.S. Cl 219/532, 99/389, 219/521, 219/536, 219/549, 219/542, 219/552,

[51] Int. Cl. H05b 3/06 [58] Field of Search 219/521, 527, 528, 529, 219/532, 536, 537, 542, 546,549, 552, 211,

[56] References Cited UNITED STATES PATENTS 1,416,481 5/1922 Longoria 219/529 1,519,176 12/1924 Troger et a1. 219/521 X 1,733,023 10/1929 Kremenezky 338/301 X 2,251,697 8/1941 Van Daam et a1 219/549 X 2,451,839 10/1948 Lemon 219/549 X 2,462,607 2/1949 Browne 2,493,542 1/1950 McGraw 338/319 2,581,212 l/1952 Spooner, Jr. et al. 338/214 X 2,706,767 4/1955 Packchanian 219/529 2,747,072 5/1956 Lawser 2,847,931 8/1958 Saint 3,002,075 9/1961 Viscos....

3,173,123 3/1965 Achncr..

3,205,341 9/1965 Bull 3,461,274 8/1969 Williams 219/542 Primary Examiner-Volodymyr Y. Mayewsky Attorney, Agent, or Firm-Craig & Antonelli [57] ABSTRACT In a heating element for a toaster the heating conductor consists of a wire wound on a core of low thermal expansion coefficient. The conductor is carried by a frame including opposite support strips between which the conductor is strung in loops without intermediate support. The core consists of twisted threads of mineral fiber. A two-compartment bread toaster needs only three such elements; the heating conductor loops of each outer element may be provided on one face only and those of the central element may be wound about both faces.

8 Claims, 7 Drawing Figures PATENTED H975 3, 870.863

FIGA' la-5' FIG.6

ELECTRICAL HEATING ELEMENT FOR BREAD TOASTER OR THE LIKE The invention relates to a heating element for bread toasters or the like, having a support on which the heating conductor is arranged in a plurality of loops.

In known heating elements the supports are made of mica plates which in external dimensions correspond approximately to the food to be toasted. A heating conductor wire is wound in strip form on these mica plates. If the heating elements are intended for a bread toaster having only one bread channel or compartment, the parallel opposite plates have a heating conductor winding only at the flat sides facing towards one another, the heating conductor wire being wound for example about projections at the two longitudinal edges of the plates, taking it to and fro. The plates are held at the two other longitudinal edges thereof with metal strips which at the same time are used for fixing the heating element in the toaster housing. For bread toasters having two parallel bread compartments, a total of three heating elements are provided, one of which is situated between the two compartments and the others one at each of the external sides of thecompartments. The externally arranged heating elements are only wound at one side, but the central heating element is wound with heating conductor wire at both sides, so that the central element radiates heat into both compartments. This central heating element also comprises an insulating mica plate as a support.

In these heating elements with very thin, strip-form heating conductor wire, care must be taken that the wire expanding when heated does not sag and come into contact with the neighbouring wire of the very closely spaced loops. Substantially two measures are taken with this in view, either insulating strips made for example of mica'being placed on the wire loops and rivetted or connected with eyelets to the plate so that the wire is clamped between strip and plate, or the plate is sub-divided into two or more individual plates and a winding is arranged on each individual plate so that the free length of the wire is reduced to such an extent that the amount by which it might sag when heated is too small to allow it to contact the nearest loop.

In another constructional form of heating element (German Laid-Open Specification 1,540,777) sagging of the heating conductor wire is prevented by making the said wire of such a thick diameter that it is selfsupporting even when it expands to a considerable extent. The wire loops are fixed at one side with eyelets, rivets or the like to an insulating strip and at their other side inserted in recesses of a second insulating strip arranged parallel thereto, so that they can be displaced in these recesses in accordance with longitudinal expansion. At their free length the loops are clamped between an insulating material panel and a further, central insulating material strip. This construction differs from the construction described previously simply in that a thicker wire is used which is held at one side only and at its other side is free to move, and also by the fact that in bread toasters with two compartments four heating elements are required instead of three.

Although both known heating elements operate satisfactorily they both have the disadvantage of comparatively high material and manufacturing cost. In both. constructional forms, the material costs are considerably influenced by the fact that each heating element has an insulating plate appropriate to the toasting area. In addition there are the costs of the additional supporting strips of insulating material. In the first constructional form the production costs are determined by considerable punching work required at the insulating material panels and also by the fact tht up to the present time it has in practice not been possible to develop a winding machine for winding the heating consuctor wire which operates in a satisfactory manner with an acceptable cost level, for which reason hand winding is much cheaper even at the present day and even when producing large numbers of items. In the second constructional form the winding operation is complicated also by the fact that the loops have to be attached by eyelets or rivets at one side during winding. The weakening of the insulating strips which results has to be compensated by a metal supporting strip. Finally here again punching work is necessary for producing the recesses for receiving the ends of the heating conductor loops which are free to move. It is true that mechanical winding of the heating conductor wire is proposed in that case, but a suitable machine woould presumably be just as expensive and just as liable to give trouble as in the case of the above-mentioned constructional form. In addition, there is the disadvantage of a longer heating up time owing to the larger wire diameter.

The inventin has an object to provide an improved heating element for a bread toaster or the like wherein sagging of the heating conductor wire is reliably prevented and yet the material and manufacturing costs can be reduced as compared with known heating elements.

This object is achieved according to the invention in that the heating element comprises a heating conductor which consists of a heating conductor wire wound on a core having a low coefficient of thermal expansion and is strung out freely in a plurality of loops between two insulating conductor support strips situated opposite one another and forming part of a frame which supports the heating conductor and is adapted in its external dimensions to the food to be toasted. The core of the heating conductor is preferably made of twisted threads consisting of mineral fibre, on which the heating conductor wire is helically wound.

A heating conductor constructed in this way can be made to extend in self-supporting manner over relatively considerable lengths without sagging when heated, since the core has only slight thermal expansion and the wound heating conductor wire will at the most be slightly increased in its coil diameter. Heating conductor wires of any diameter can be used, more especially with the advantageous small diameter of the first mentioned conventional constructional form with the consequence of shortening the heating-up time. Owing to the properties of the heating conductor described, it is sufficient to support it simply by frame members so that the conventional plates can be omitted, likewise the central fixing strips of insulating material which have hitherto been provided, so that there is a considerable saving in material. Furthermore the use of eyelets or rivets to secure the heating conductor is no longer required, so that manufacturing costs can be reduced there also.

A further surprising advantage of the heating element provided by the invention is that in bread toasters having two toasting compartments only one central heating element is required, since owing to the frame-shaped 3 construction of the support the heating conductor radiates at the same time to both sides. This also means that for bread toasters having more than one toasting compartment all three heating elements areofthe same form, so that there is a simplification in manufacturing operations. I

The frame preferably comprises two parallel supporting strips which connect the conductor support strips to which the heating conductor loops are fixed. Whereas the conductor support strips are advantageously formed of mica strips the parallel supporting strips can be of metal on which the mica strips are secured on the one hand and means are provided on the other hand for fixing the heating element on the toaster housing. A conventionalmeans for preventing contact can also be provided on these supportingstrips and in respect of the outer heating elements a reflector or heat insulator can be provided for'protecting the housing from excessive heating.

The heating conductor consisting of core and heating wire can either be wound stepwise about the two flat sides of the conductor support strips or wound stepwise only at one flat side of the conductor support strips. The first form is suitable more especially for a central heating element for bread toasters having more than one toasting compartment, whereas the second form is intended for externally arranged lateral heating elements for toasters having one or more toasting compartments. However the heating conductor is wound, it can be wound mechanically without difficulty in contrast to what has been the case hitherto, since the loop form is extremely simple. dr

Further details, features and advantages of the invention will become apparent from the following description of one preferred constructional form with reference to the accompanying drawings in which:

FIG. 1 is a view of a constructional form of heating element;

FIG. 2 is a section through a heating conductor;

FIG. 3 shows a cross-section througha bread toaster with two toasting compartments I FIGS. 4 vto 6 show connection diagrams for a toaster having two toastingcompartments'and FIG. 7 illustrates a further embodiment of the heating element.

Referring first to FIG. 1, the heating element, which as a whole is given the reference numeral 1, comprises a frame 2 which is used as a support for a heating conductor 3. This heating conductor 3 is shown in crosssection in FIG. 2. It comprises a core 4 which has a low coefficient of thermal expansion, and a heating conductor wire 5 wound helically on the said core. The core, in the illustrtaed constructional example, is formed of three strands 6 composed for example of mineral fiber material, which are twisted together. Owing to the low thermal expansion of the core, substantially the only modification in the heating conductor when heated is that the heating conductor wire 5 slightly increases in its diameter.

The heating conductor 3 is wound on the two lateral frame members used as conductor support strips 7-, as FIG. 1 shows. These parallel frame members consist of an insulating material, for example being made of mica strips or the like. Instead of course it would be possible to use an insulating rod system or the like such as Ms tratedin FIG. 7. If mica strips are used, these can coma constructional form of prise notches or projections at their external sides to holds the individual loops of the winding in position.

The frame 1 is completed by supporting strips 8 which connect the conductor support strips 7 to one another.

These supporting strips are madepreferably of metal which may be profiled for stiffening purposes and covered with insulating material which may be braided or moulded. The conductor support strips 7 are secured to these supporting strips by means of eyelets, rivets 9 or by electrical w elding.

In the constructional form shown in FIG. 1, the heating conductor 3 is wound in stages round the conductor support strips 7. Instead of this, the heating conductor may be wound in stages only at one flat side of the conductor support strips 7, taking it to and fro constantly. The spacing of the individual heating conductor loops decreases in a downward direction from above, in order to obtain uniform heating of the food being toasted. The supporting strips 8 are used for securing the heating element within the toaster housing, details of whichhave been omitted from the illustration for the sake of clarity.

FIG. 3. shows a diagrammatic section through a bread toaster with two toasting compartments. In the housing 10, two insert slots 11 are provided for the two toasting compartments. The food to be toasted 12, for example slices of bread, are situated on supporting surfaces 13 which at the same time,.in known manner, eject the food when toasted. For such a toaster a total of three heating elements are required, of which the two external heating elements 14 radiate only inwards, whereas the centralheating element ISradiates in both directions. The heating elements 14, for example, can be wound only at one side with the heating conductor, whereas the central heating element 15 is wound, for example, all round. To prevent the external walls of the housing 10 from being heated too strongly,'the external heating elements l4'can have reflectors or heat insulating means 16 associated with them. These reflectors are not particularly'intended to reflect all the radiated heat arriving at them, but are rather intended to shield the housing from some of the heat.

FIGS. 4 to 6 show the electrical connection possibilities for a bread toaster with two toasting compartments. FIG. 4 shows the ideal state where each heating element is designed for a voltage of 220'volts. There is no difference in the construction of the lateral heating elements 17 and the central heating element 18. The heating elements are connected in parallel to the mains voltage.

In the series connection arrangement shown in FIG. 5 the lateral heating elements 19 are designed for a power of 250 watts and the central heating element 20 for a power of 360 watts. There is a difference in the construction of these heating elements in that the external heating elements 19 are wound only at one side whereas the central heating element 20 is wound all round. I

Finally, in the arrangement shown in FIG. 6 the two lateral heating elements 21 are connected in series and are connected to the mains voltage in parallel with the central heating element 22.

What is claimed is: 1. A heating element for a bread toaster comprising an electric heating conductor including a core of a low coefficient of thermal expansion material, said core consisting of threads of mineral fiber material twisted together, electric conducting heating wire helically wound about said core, and means for providing electrical connection of said electric heating conductor, said electric heating conductor being sufficiently rigid to maintain its shape during 5 heating, and

an open framework means for supporting a plurality of loops of said electric heating conductor, said framework means consisting of two spaced insulating support means for supporting said plurality of loops, each of said two insulating support means having a first longitudinal dimension much greater than the width, and two spaced rigid connecting means for holding said two insulating support means in stationary spaced relationship, said two connecting means each having a second longitudinal dimension much greater than the width thereof, and each of said two insulating support means being fixed at respective opposite ends of each of said two spaced connecting means such that said two insulating support means are fixed apart from one another by a distance equal to said second longitudinal dimension of said two connecting means to form an open rectangular area without any structure therebetween, said electric heating conductor being only in contact with said two spaced insulating means of said open framework means and extending across said open framework means between said two spaced insulating means to radiate heat in both directions outwardly from the plane of the open area of said open framework means,

wherein said two spaced connecting means include means for securing the heating element to a housing of a toaster.

2. A heating element according to claim 1, wherein said two spaced insulating support meansare each formed of mica strips.

3. A heating element according to claim 1, wherein said two spaced insulating support means are each formed of insulating rods.

4. A heating element according to claim 1, wherein said two spaced insulating support means are each formed of metal strips covered with insulating material.

5. A heating element according to claim 1, wherein said two spaced connecting means are formed of metal.

6. A heating element according to claim 1, wherein said electric heating conductor is looped in stages about both sides of said framework means in contact with said two spaced insulating support means.

7. A heating element according to claim 1, wherein said electric heating conductor is looped in stages on only one side of said framework means in contact with said two spaced insulating support means.

8. A heating element according to claim 1, wherein each of said two insulating support means includes at least one notch and projection at an edge thereof to hold individual ones of said plurality of loops.

Claims

1. A heating element for a bread toaster comprising an electric heating conductor including a core of a low coefficient of thermal expansion material, said core consisting of threads of mineral fiber material twisted together, electric conducting heating wire helically wound about said core, and means for providing electrical connection of said electric heating conductor, said electric heating conductor being sufficiently rigid to maintain its shape during heating, and an open framework means for supporting a plurality of loops of said electric heating conductor, said framework means consisting of two spaced insulating support means for supporting said plurality of loops, each of said two insulating support means having a first longitudinal dimension much greater than the width, and two spaced rigid Connecting means for holding said two insulating support means in stationary spaced relationship, said two connecting means each having a second longitudinal dimension much greater than the width thereof, and each of said two insulating support means being fixed at respective opposite ends of each of said two spaced connecting means such that said two insulating support means are fixed apart from one another by a distance equal to said second longitudinal dimension of said two connecting means to form an open rectangular area without any structure therebetween, said electric heating conductor being only in contact with said two spaced insulating means of said open framework means and extending across said open framework means between said two spaced insulating means to radiate heat in both directions outwardly from the plane of the open area of said open framework means, wherein said two spaced connecting means include means for securing the heating element to a housing of a toaster.

2. A heating element according to claim 1, wherein said two spaced insulating support means are each formed of mica strips.